Fix EventLogger in .NET 4.5.2

Author: BrennanConroy

src/Microsoft.Extensions.Logging.EventSource/EventSourceLogger.cs

@@ -44,6 +44,7 @@ public EventSourceLogger(string categoryName, int factoryID, LoggingEventSource
 
         public bool IsEnabled(LogLevel logLevel)
         {
+            _eventSource.VerifyLevel();
             return logLevel >= Level;
         }
 

src/Microsoft.Extensions.Logging.EventSource/LoggingEventSource.cs

@@ -106,6 +106,7 @@ public class Keywords
         private string _filterSpec;
         private EventSourceLoggerProvider _loggingProviders;
         private object _lockObj = new object();
+        private bool _checkLevel;
 
         internal EventSourceLoggerProvider CreateLoggerProvider()
         {
@@ -226,9 +227,19 @@ protected override void OnEventCommand(EventCommandEventArgs command)
         private void SetFilterSpec(string filterSpec)
         {
             _filterSpec = filterSpec;
-            for (var cur = _loggingProviders; cur != null; cur = cur.Next)
+            _checkLevel = true;
+        }
+
+        [NonEvent]
+        internal void VerifyLevel()
+        {
+            if (_checkLevel)
             {
-                cur.SetFilterSpec(filterSpec);
+                for (var cur = _loggingProviders; cur != null; cur = cur.Next)
+                {
+                    cur.SetFilterSpec(_filterSpec);
+                }
+                _checkLevel = false;
             }
         }
     }

test/Microsoft.Extensions.Logging.EventSource.Test/EventSourceLoggerTest.cs

@@ -23,7 +23,7 @@ public void Logs_AsExpected_WithDefaults()
                 factory.AddEventSourceLogger();
 
                 var listenerSettings = new TestEventListener.ListenerSettings();
-                listenerSettings.Keywords = EventKeywords.None;
+                listenerSettings.Keywords = (EventKeywords)(-1);
                 listenerSettings.FilterSpec = null;
                 listenerSettings.Level = default(EventLevel);
                 testListener.EnableEvents(listenerSettings);